1. Field of the Invention
The invention relates to a hearing assistance system comprising a wireless remote control for transmitting control commands as an amplitude modulated radio frequency signal, a radio frequency (RF) power detector for outputting a signal representative of the power envelope of the RF signal received by an antenna of the RF power detector, an audio signal processing unit, and means worn to be worn at or at least in part in the user's ear for stimulating the user's hearing according to audio signals processed in the audio signal processing unit. The invention also relates to a method of operating such a hearing assistance system.
2. Description of Related Art
Hearing instruments comprising means for stimulating the user's hearing according to audio signals processed in the audio signal processing unit of the hearing instrument often are used together with a dedicated, usually wireless, remote control in order to allow the user to interact with the hearing instrument via an interface which is more convenient and has more features than the one provided by the hearing instrument. Examples of such systems are described in European Patent Applications EP 1 420 611 A1 and EP 1 326 480 A2, German Patent Application DE 100 48 338 A1, U.S. Pat. Nos. 6,816,600 and 4,947,432.
Such hearing assistance systems in addition often comprise a remote device spaced apart from the hearing instrument for establishing a wireless link between the remote device and the hearing instrument for transmitting audio signals from the remote device to the hearing device.
Examples of such hearing assistance systems are binaural hearing aids (in this case the remote device is a hearing instrument which is worn at the other one of the user's ears, with both hearing instruments being hearing aids comprising a microphone and an output transducer); in this case the link may serve as a bi-directional data link for exchanging audio signals, control data, and/or commands between the hearing aids.
Other examples of such a hearing assistance systems are CROS or BiCROS systems (in this case the remote device is a wireless microphone worn at the other one of the user's ears). In a CROS (also spelled CROSS) system the hearing instrument does not comprise a microphone, while in a BiCROS (also spelled BiCROSS) system the hearing instrument comprises a microphone, depending on whether the ear at which the hearing instrument is worn needs hearing assistance or not. In both cases the ear at which the wireless microphone is worn is essentially unable to be aided by a hearing instrument.
According to further examples of such hearing assistance systems the remote device is a remote control for the hearing instrument (in this case the link is for transmitting control data and/or commands from the remote control to the hearing instrument), an external microphone worn by another person (for example a teacher) or an external microphone worn by the user at a place other than the ears, or a device for wireless transmission of audio signal from a external audio signal source, such as a telephone, a television, an external microphone, a hi-fi-system, etc.
Generally, the receiver unit for the wireless link could be integrated within the hearing instrument/hearing aid, or the receiver unit could be a separate device which is mechanically and electrically connected to the hearing instrument/hearing aid, usually via an “audio shoe” in order to provide the audio signals received over the wireless link to an audio input of the hearing aid.
In such known systems the wireless link from the remote device to the receiver unit included in or connected to the hearing instrument may be heavily disturbed if a source of interfering radio frequency signals comes close to the hearing instrument. A typical example for such interfering radio frequency source is a mobile phone. Typically, a mobile phone transmits TDMA (time division multiple access) signals, for example according to the GSM (global system for mobile communications) standard. In this case transmission from the mobile phone occurs periodically, with only ⅛ of the time being used for transmission. A similar periodic transmission scheme is found in cordless telephone systems using the DECT standard; also in this case only a relatively small fraction of each period is used for transmission. This applies similarly also to devices using the Bluetooth standard.
If such interfering radio frequency source is brought very close to the hearing instrument worn had the user's ear, the link between the remote device and the hearing instrument may break down, what is very inconvenient for the user. Such radio frequency sources may be considered as “burst interferes”.
However, also systems which do not include such remote device may suffer from interfering radio frequency signals which may affect the audio path of the hearing instrument, thereby producing unwanted audio artifacts.
Examples of wireless links for binaural hearing aid systems are found in U.S. Pat. No. 6,549,633 and U.S. Patent Application Publication 2004/0037442 A1.
According to U.S. Patent Application Publication 2005/0117764 A1 the use of a DECT or GSM phone at one of the two sides of a hearing aid set is detected by analyzing the level difference between the left ear and right ear hearing coil in order switch the respective hearing aid to a phone mode.
According to U.S. Pat. No. 6,587,568 and European Patent Application EP 1 501 200 A2 a hearing aid is capable of recognizing periodic RF (radio frequency) interference signals, for example from mobile phones, with the gain of the hearing aid being synchronized to the periodicity of the RF interference signals, so that the gain of the hearing aid is reduced or even set to zero during the presence of an interfering RF burst. According to U.S. Patent Application Publication 2003/076974 A1 a hearing aid is capable of detecting the presents of characteristic RF interference signals in order to not only switch the gain of the hearing aid accordingly but also to switch other parameters, such as the filter band width, of the hearing aid accordingly. Thereby specific auditory scenes can be recognized, in particular the use of a telephone, in order to adapt the operation mode of the hearing aid accordingly.